In capacitive sensor devices, by means of which an approach and/or a contact shall be detected, it may be required that the capacitive sensor device has to be calibrated once or in predefined temporal intervals. For example, a calibration of the capacitive sensor device may be required to ensure a high accuracy of detection also in changing ambient conditions.
A problem in the calibration of capacitive sensor devices exists in that the sensor device may not be calibrated at each arbitrary point in time, for example when objects are in the proximity of the capacitive sensor device, i.e. in the proximity of the measurement electrodes of the capacitive sensor device. The objects arranged in the proximity of the sensor device may negatively affect the calibration of the sensor system so that the sensor device in the end is calibrated erroneous. Therefore it is desirable to calibrate the sensor device at a point in time at which no objects affecting the calibration procedure are arranged in the proximity of the capacitive sensor device.
In addition it is desirable to calibrate a capacitive sensor device directly after the activation and after the power-on, respectively, of the capacitive sensor device so that, for example, a capacitive sensor device provided in an electric handheld device may be used directly after power-on of the handheld device. According to prior art the capacitive sensor device is calibrated directly after power-on of the electric handheld device or after the activation of the capacitive sensor device within a predefined period of time, approximately one second. In order to be able to carry out an orderly calibration the user is not allowed to handle the handheld device during this period of time since this in turn would negatively affect the calibration. The user of the handheld device may be informed, for example via a display device that the capacitive sensor device is in a calibrating phase. In doing so, however, it is not ensured that the user does not still manipulate the handheld device during the calibrating phase. In addition, such a calibration method is unacceptable, if only for ergonomic reasons.
A further possibility known in prior art for calibrating a capacitive sensor device is to carry out the calibration when the raw data of the capacitive sensor device have not changed or only have changed very little during a predefined period of time, for example because the user has deposited the electric handheld device. However, it is a disadvantage with this method that it cannot be ensured that a calibration of the sensor system is carried out at all, because it is not ensured that the raw data of the sensor device do not change or only change very little during a predefined period of time. In addition it is disadvantageous that the raw data of the capacitive sensor device are processed in an uncalibrated manner by all means until the point in time, in which a calibration is carried out, which may result in erroneous detections of approaches and/or contacts.
In a further solution known from prior art the user of an electric handheld device activates the calibrating action. For example, this may be carried out by means of actuating a button specifically provided to do so. Alternatively, the calibrating action also may be activated by carrying out predefined gestures, wherein such gestures should be provided, which also may be recognized from the initially uncalibrated raw data of the sensor device. Such gestures, for example, may be swiping gestures or a quick removal of a finger put down on the electric handheld device prior to that. This method has the disadvantage that, because the calibration is initiated by the user, the sensor device is not calibrated during a longer period of time, because the user may have forgotten to initiate the calibration or does not know that he/she has to carry out a calibration. A further disadvantage is that a carrying out of the gestures provided for the activation of the sensor system may result in an unintended calibration and that it is not ensured, that for example fingers or the hands do not negatively affect the calibration.